Northeastern Argentina’s history is inseparable from the two great rivers—the southward-flowing Uruguay and Paraná—that eventually unite to form the Río de la Plata estuary.

Between the rivers, the Mesopotamian provinces of Entre Ríos, Corrientes, and Misiones form a virtual island where, in pre-Columbian times, Guaraní-speaking Indians subsisted on beans, maize, and root crops like manioc and sweet potatoes. River fish also played an important role in the diet, though wild game was less abundant than in the southerly pampas.

On the Paraná’s right bank, and northward into the Gran Chaco’s “green hell,” the aboriginal inhabitants were mostly hunter-gatherers who, like the Guaraní, also relied on fishing.

More numerous than the nomadic inhabitants of the pampas, the semi-sedentary Guaraní attracted the attention of early Spanish explorers. In 1537, Pedro de Mendoza’s lieutenant Pedro de Ayolas ascended the Paraná to found the city of Asunción, in present-day Paraguay, where the Guaraní provided them food and other essentials. From Asunción, Spanish settlement proceeded south into Corrientes and Santa Fe.

The most effective colonizers, though, were the Jesuits who congregated the Guaraní into permanent settlements and taught them the Spanish language, Catholic religion, and even skilled trades like violin-making. At the same time, many Guaraní served as unskilled labor on the Jesuits’ yerba mate (Paraguayan tea) plantations and cattle ranches.

The Jesuits’ success provoked Portuguese slave raids from Brazil and political intrigues in Spain that brought their expulsion from the Americas in 1767, and lush subtropical forests soon covered their monumental sandstone missions.

In postcolonial times, Argentine Mesopotamia became an area of caudillos (provincial strongmen)—most notably Justo José Urquiza, who helped topple the Rosas dictatorship—and then the staging point for the War of the Triple Alliance against Paraguay in the 1870s. The west bank of the Paraná, though, surged ahead economically as the river port of Rosario became a major export point for grains from the pampas.

Today, Mesopotamia, the Chaco provinces, and even the provincial capital of Santa Fe lag behind Rosario in their economic development and cultural life.